Electrically conductive oxide semiconductors have in recent years attracted attention as materials for forming optically transparent, transparent electrodes or the active (channel) layer of thin-film transistors (abbreviation: TFT) or other semiconductor devices. Thin-film transistors that utilize an oxide semiconductor as the active layer are being actively applied to flat panel display devices like liquid crystal display (abbreviation: LCD) devices and organic electro-luminescent (abbreviation: EL) devices. Moreover, transparent electrodes containing an oxide semiconductor as a component have been applied to flat display panels and other flat panel display devices, as well as to touch panels.
In these fields of industrial application of electrically conductive oxide semiconductors, in order to reduce the RC delay of signal transmission, ohmic electrodes composed of metal materials of high electrical conductivity and low electrical resistance are used for the interconnections and electrodes of the oxide semiconductor. The prior art uses, for example, aluminum (element symbol: Al), aluminum alloy, molybdenum (element symbol: Mo), and the like. Further, there have been proposed electrodes and interconnectors formed by laminating dissimilar metal layers of alloys of titanium (element symbol: Ti) or aluminum and silicon (element symbol: Si). Recently, moreover, a technique has been tried that forms an oxide semiconductor ohmic electrode from copper (element symbol: Cu), which has low electrical resistance.
For example, regarding a thin Film Transistor (abbreviation: TFT) used in a liquid crystal display device (abbreviation: LCD), technologies are available for using copper alloy to form the ohmic electrodes constituting a source electrode and a drain electrode, as well as interconnectors (see Patent document 1 to 7). In particular, Patent document 5 teaches that by using a copper alloy obtained by adding a suitable additive element to copper, oxidation of the copper is inhibited by a metallic oxide film formed by the additive element, so that ohmic electrodes of low electrical contact resistance and copper interconnectors of small RC delay are furnished.
It has been suggested that manganese (element symbol: Mn) is preferable as the additive element (see Patent document 5). Non-patent document 1 teaches a technique for forming a copper electrode on a thin-film transistor that uses an electrically conductive oxide semiconductor as an active (channel) layer. Specifically, copper-manganese (Cu—Mn) alloy is used when forming a copper electrode on a thin-film transistor using amorphous gallium oxide-indium-zinc (Ga—In—Zn—O) as the active layer.